title: Downregulation of Stat3 in melanoma: reprogramming the immune microenvironment as an anticancer therapeutic strategy.
abstract: Persistent activation of the transcription factor, signal transducer and activator of transcription 3 (Stat3) has been shown to mediate several oncogenic features in many types of cancers, including melanoma. In this study, we investigated whether lentiviral (LV) delivery of Stat3-targeting short hairpin RNA (shRNA; LV-shStat3) to K1735-C4 melanoma cells modulates antitumor immunity. Three shStat3 sequences, starting at the position 446, 830 and 1412, were cloned into a mir30 cassette. A shRNA with scrambled sequence served as a control. Transduction with LV-shStat3 resulted in downregulation of Stat3 in vitro. The latter coincided with low cell viability, a reduced expression of survivin and matrix metalloproteinase (MMP)-2. A single injection of LV-shStat3 in K1735-C4 tumors efficiently downregulated Stat3 in vivo and resulted in reduction of both vascular endothelial growth factor secretion and in myeloid-derived suppressor cell (MDSC) numbers. In contrast, we observed an increase in interleukin-6 and interferon-γ secretion, mature dendritic cells (DCs) and CD8(+) T cells. Both DCs and CD8(+) T cells displayed enhanced activity, whereas granulocytic MDSCs lost their suppressive capacity upon Stat3 downregulation. Importantly, a single injection of LV-shStat3 was sufficient to reduce tumor growth, hence prolong survival of tumor-bearing mice. These data demonstrate that Stat3 downregulation in melanoma reinvigorates existing antitumor immunity.
authors.affiliation: Laboratory of Molecular and Cellular Therapy, Department of Immunology-Physiology, Vrije Universiteit Brussel, Jette, Belgium.
authors.forename: P U
authors.initials: PU
authors.lastname: Emeagi
authors.forename: S
authors.initials: S
authors.lastname: Maenhout
authors.forename: N
authors.initials: N
authors.lastname: Dang
authors.forename: C
authors.initials: C
authors.lastname: Heirman
authors.forename: K
authors.initials: K
authors.lastname: Thielemans
authors.forename: K
authors.initials: K
authors.lastname: Breckpot
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D002470:Cell Survival; D015536:Down-Regulation; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D005822:Genetic Vectors; D057809:HEK293 Cells; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins / Q000378:metabolism; D016086:Lentivirus / Q000235:genetics; D020778:Matrix Metalloproteinase 2 / Q000378:metabolism; D008545:Melanoma / Q000235:genetics* / Q000276:immunology / Q000378:metabolism / Q000628:therapy; D008546:Melanoma, Experimental / Q000235:genetics* / Q000276:immunology / Q000378:metabolism / Q000628:therapy; D051379:Mice; D008810:Mice, Inbred C57BL; D034741:RNA, Small Interfering / Q000008:administration & dosage; D012097:Repressor Proteins / Q000378:metabolism; D050796:STAT3 Transcription Factor / Q000235:genetics* / Q000378:metabolism; D000077022:Survivin; D014161:Transduction, Genetic; D014407:Tumor Cells, Cultured; D059016:Tumor Microenvironment / Q000276:immunology*
chemical_list: C117749:Birc5 protein, mouse; D051034:Inhibitor of Apoptosis Proteins; D034741:RNA, Small Interfering; D012097:Repressor Proteins; D050796:STAT3 Transcription Factor; D000077022:Survivin; D020778:Matrix Metalloproteinase 2